Auditory P300 and Eye Tracking Dysfunction in Schizophrenic Pedigrees

From the University Department of Psychiatry, Royal Edinburgh Hospital, and the Medical Research Council Human Genetics Unit, Western General Hospital (Drs Blackwood, St Clair, and Muir), and the University Department of Statistics (Mr Duffy), Edinburgh, Scotland.

• Several psychophysiological abnormalities associated with schizophrenia have been proposed as genetic trait markers of vulnerability to the disorder. Smooth pursuit eye tracking dysfunction and abnormal long latency eventrelated potentials are the most promising candidates. Both are independent of the effects of psychotropic medication or mental state at the time of testing, and twin studies demonstrate that each has a high level of heritability. Having recorded smooth pursuit eye tracking and event-related potentials in 20 high-density schizophrenic families, we find abnormalities in one or both measures in most of the families studied. The abnormalities, when present, occur in the family members with schizophrenia and other forms of functional psychosis, and they have a bimodal distribution with approximately half the nonschizophrenic relatives also showing eye tracking dysfunction and/or abnormal eventrelated potentials. Some of these relatives had psychiatric symptoms; others were normal. Our results suggest that psychophysiological examination can help to clarify the boundaries of schizophrenia spectrum disorder. By helping to decide the phenotypic status of nonschizophrenic family members, this should increase the power of DNA linkage studies.